AQA GCSE Biology

Ecosystems & food chains

AQA GCSE Biology revision on Ecosystems & food chains. Aligned to the AQA GCSE Biology 8461 specification. This bank has 25 practice questions on this topic.

Sample questions (3 of 25)

  1. Question 1

    What is the original source of energy in (almost) every food chain?

    • A) Plants
    • B) The Sun
    • C) Decomposers
    • D) Carnivores
    Show answer

    Answer: The Sun

    Energy flow: Sun -> producers (plants) -> primary consumers (herbivores) -> secondary consumers (carnivores) -> tertiary consumers. Each step loses ~90% of the energy as heat - that's why food chains rarely exceed 4-5 links.

  2. Question 2

    Decomposers in an ecosystem play the role of...

    • A) Eating plants
    • B) Breaking down dead matter, recycling nutrients to soil
    • C) Pollinating flowers
    • D) Producing oxygen
    Show answer

    Answer: Breaking down dead matter, recycling nutrients to soil

    Without decomposers, nutrients (carbon, nitrogen, phosphorus) would stay locked in dead organisms. Decomposers break dead matter down into simpler compounds + soluble minerals, which plants absorb via roots and reuse. The CARBON CYCLE and NITROGEN CYCLE both rely on decomposers. They're the unsung heroes of every ecosystem.

  3. Question 3

    A biotic factor in an ecosystem is one that involves...

    • A) Living organisms
    • B) Temperature only
    • C) Soil pH
    • D) Rainfall
    Show answer

    Answer: Living organisms

    Biotic factors: predators, prey, competitors, pathogens. Abiotic factors: temperature, light, water, pH, oxygen levels, mineral content. Both influence where + how well organisms survive. Example: a polar bear is limited by abiotic (cold preferred, sea ice needed) AND biotic (seal availability).

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